Method of preserving rubber latex



Patented Jan. 15, 1929.

UNITED STATES PATENT. OFFICE.

JOHN MCGAVACK, OF JACKSON HEIGHTS, NEW YORK, D ROY A. SHIVE, OF BELLE- MOOR, DELAWARE, ASSIGNORS TO THE NAUGATUCK CHEMICAL COMPANY, OF

NAUGATUCK, CONNECTICUT, A CORPORATION OF CONNECTICUT.

METHOD or rn'nsnnvmo RUBBER :hA'rnx.

No Drawing. riginal application filed April 8, 1927, Serial No.182,174. Divided and this application filed March 2, 1928.

It has generally been recognized that rubber latex at the time of its exudation from r the tree has an alkaline reaction which very speedily changes to an acid reaction. To preserve latex in an uncoagulated condition it has been customary to maintain the latex in an alkaline state by the addition, of an alkali or basic substance. This art of pre serving latexby maintaining an alkaline con- 1 dition therein has been known'for a good many years and has been regarded as the only means whereby uncoagulated {rubber latex can be safely shipped from the Plantation countries to manufacturing countries. The bulk of such: preserved latex contains ammonia as the alkaline substance or preservative or stabilizer. It has never been possible, and in fact has never been suggested that latex may also be preserved against all semblance of coagulation and yet show an acid reaction.

The present invention is concerned with the preparation of what may be briefly termed a stable acid latex. The invention aims to provide methods for treating latex to render it stable both at the neutral point and on the acid side of neutrality. The invention further includes means for treating rubber'latex so that it will, when converted into rubber, furnish a product of high plasticity, improved rate of drying, and enhanced cohesiveness. The invention further aims to providea stable latex adapted for use 'where a latex having a slightly acid reaction is desirable or necessary.

Briefly stated the 1 invention consists in treating rubber latex with an agent capable of stabilizing-the latex and preventing its coagulation at the neutral point as well as on the acid side of neutrality, and with an agent which will carry the reaction to the acid side of neutrality; The invention includes within its scope the treatment of natural rubber latex as ittis received after tapping, as well as latex which has been preserved by means of the addition of an alkaline preservative, stabilizer, etc. Although particular embodiments are given, it. is with the understandin that'these are to be re- I I o limitations.

garded in the lig t of examples, and not as Serial No. 258,683.

This application is a division of our copending application Serial No. 182,174, filed April 8, 1927. 1

As one illustration of the invention, 1000 cos. of natural latex are treated with 3-5 grams of the reaction product of cinnamic acid, butyl alcohol and sulphuric acid or chlor sulphonic acid. To the latex is also added 10-15 cos. of 38% formaldehyde solution. This latex is stable and has an acid reaction. When treating ammonia preserved latex instead of natural untreated latex, it is necessary to remove the ammonia or nullify its effect. This may be accomplished by air blowing, by neutralizing, by precipitating the hydroxyl ions as insoluble hydroxides formation of complex compounds with the ammonia or in any other suitable method.

Prior to the disposal of the ammonia, or

the reaction product of para cresol and oleic acid obtained in the presence of sulphuric or chlorsulphonic acid are added per thousand cos. of 38% latex. "After the addition, the ammonia may be removed by an air blowing treatment. After this has been completed the latex is then treated with about 40 cos. of 38% formaldehyde. The product is a suitable latex; havin an acid reaction, that is its pH may vary ietween 4.5 and 7, depending upon the amount of formaldehyde added.

Instead of blowing as a method of 'removing the ammonia, the latter may be neutralizediwith a weak acid such as acetic acid or'boric acid and the addition of the acid continued until the proper hydrogen ion concentration has been reached, or is increased above 1X10". In this instance an appreciable quantity of salts will be formed as a result of the reaction of the acid and the ammonia, and care must be taken to have a suflicient amount of the stabilizer agent present when the acid is introduced. Otherwise the salts formed will ionize and-tend to disturb the latex equilibrium. In cases where salt for-.

' mation, and the presence of salts in the latex itis not desirable to have inorganic salts thus formed, formaldehyde may be added to the ammonia latex instead of the acetic acid or other acid. In this instance the amount of formaldehyde should be sufficient to react with the ammonia andto give the desired hydrogen ion concentration. By this method, thelatex may be brought to a very strong acid concentration. or at least to a point as low as pH4.5. To illustrate more specifically, 1000 ccs. of ammonia preserved latex containing 301 2v of rubber are treated with 8 grams of the reaction product obtained from the condensation of butyl alcohol with cinnamic acid in the presence of sulphuric acid. To the latex are added 30-35 ccs. of 36% formaldehyde solution. It is believed that the ammonia reacts with part of the formaldehyde to form hexamethylene tetramine. A portion of the formaldehyde may react with the proteins in the latex to dispose of the free amino groups by adding them together in a methylene linkage structure thus freeing the carboxyl groups of the proteins. It is to be understood, however, that these reactions are suggested explanations of what might take place, and the merits of the invention are not dependent upon the correctness or incorrectness of the above theory.

The products obtained in accordance with the above examples may be generally termed as stable acid latices. Their major properties are in most respects the same as those of alkaline preserved latex. -There are, however, important distinctions besldes the acid reaction. These acid latices have the property of drying more rapidly when spread on a surface than ammonia preserved latex, and they give a film which is less tou h, in other words has more of the rubber property.

The magnification of therubber property -may be due to the fact that changes are wrought upon the non-rubbers, presumably the proteins, which are known to lack the elasticity ofthe rubber hydrocarbon. Regardless ofwhat takes place, the fact remains that rubber, films and coatings derived from stable acid latex dry more rapidly, absorb less water, and are more rubbery than films or layers of rubber (leri vedfrom ammonia preserved or other alkaline treated latex.

It becomes apparent, in view of the above,

that a new class of stabilizing agent or preservative has been discovered. This class includes the Twitchell type of compound. Stabilizing agents of the kind mentioned in the above examples may be obtainedby the sulphonation of aromatic phenols and hydrocarbons,- in the )resence of unsaturated aliphatic acids. hese reaction products may be powder like oroil like masses. More spe-' cifically, one such stabilizing agent may be made by treating pura cresol and oleic acid with sulphuric acid or chlor sulphonic acid.

Other types of stabilizing agents comprise 'sonal differences. etc.

aromatic acids sulphonated in the presence of aliphatic alcohols, one illustration of which ,has been given in one of the above examples. Other materials which may be used to stabilize latex on the acid side of neutrality are the reaction products obtained by condensing aromatic hydrocarbons such as anthracene, naphthalene, etc., with aliphatic alcohols, such as propyl, iso propyl, butyl, amyl, in the presence of sulphuric acid," chlor sulphonic acid or fuming sulphuric acid. It is of course understood that some of these compounds will have a greater stabilizing effect than others, and it may be necessary to use greater amounts of some of 8 them. Consideration must also be taken of .the fact that the latex itself may vary somewhat, due to fluctuations in ammonia content, condition of the proteins and the sea- Adjusting the percentage of stabilizing agent, however, is a simple matter of using more or less of the. agent, as required.

The stable acid latex prepared according to any of the above examples may be used as such in cases where it is desired to have an acid reaction. The latex may be converted into rubber by coagulation, drying, or spraying, etc. The rubber thus produced is considerably more plastic on the mixing mill than rubber similarly prepared from alkaline preserved latex. This improvement is especially noticeable in contrast with rubber derived from latex reserved with a nonvolatile alkali. In instances where it is desired to form a stable acid latex from a latex which has been preserved with a nonvolatile alkalior alkaline material, it may of course be impossible to avoid having an increased percentage of salts, such as those resulting from neutralizing the alkaline compound.

In the appended claims theword uncoagulated is used to indicate the absence of any coagulation, and. the expression excludes those partial stages of coagulation whichare not visible to the naked eye, but may be clearly seen under a microscope. The word uncoagulated is used as signifying the absence of any coagulation. The stabilizing agents are defined in the claims as sulphonic alkyl 1 aryl reaction products and thisterm is to be understood as generic to the reaction products described above and including sulphuric. sulphonic or chlorsulphonic reaction products of alkyl and aryl hydrocarbons, alcohols and acids. The word sulphonic is used as descriptive of'the reaction product, although it is understood that the products need not and may not necessarily be strictly sulphonates. v V

Having thus described our invention, what we claim and desire to protect by Letters Patent is:

1. A. method of treating latex which comprises treating latexWvith a sulphoni'c alkyl not and formaldehyde in quantities sufficient to nullify the effect of the ammonia and to impart to the latex a pH of less than 7 4. A method of converting stable uncoagulated ammonia latex into stableuncoagu lated acid latex which comprises adding to the latex a sulphonic alkyl aryl reaction product, driving off the ammonia, and adding formaldehyde to the latex to impart a pH between 7 and 4.5.

'59 A method of converting stable uncoagulated ammonia latex into stable uncoagulated acid latex which comprises adding to the latex a sulphonic reaction productof butyl alcohol and cinnamic acid, driving ofi the ammonia, and adding formaldehyde to the latex to impart a pH between 7 and 4.5.

Signed at New York, county and State of New York, this 6th day of February, 1928. JOHN MOGAVACK.

Signed at Wilmington, county of New Castle, State of Delaware, this 24th day of February, 1928.

ROY A. S HIVE. 

